Conventionally, registered vehicles in every country in the world are provided with numbers that are unique to the respective vehicles, and each vehicle is provided with number plates including such a number on its front and back sides. However, since the number of stolen vehicles has increased recently, and the number plates of such stolen vehicles can be replaced by those of other vehicles, the detection of the stolen cars has become difficult. Moreover, the cases where only number plates are stolen for criminal purposes also are increasing.
In order to solve these problems, it has been proposed to attach a sticker having vehicle information and a counterfeit-preventing function to an inner surface of a window of the vehicle. As such a sticker that is attached to a transparent object from a back side thereof so as to be observed from a front side thereof, for example, a vehicle-identifying sticker including a print layer showing vehicle information such as text information and a bar code on a support, and a self-destructive layer containing a hologram and the like formed on an upper surface of the print layer, which cannot be tampered, is proposed (for example, see Patent Document 1). This vehicle-identifying sticker is provided with a pressure-sensitive adhesive layer on the self-destructive layer side, and is attached to an object via the pressure-sensitive adhesive layer. If the thus once-attached vehicle-identifying sticker is peeled off, the self-destructive layer is destroyed, and thus the vehicle-identifying sticker cannot be reused.
In addition, as such a sticker that is attached to a transparent object from a back side thereof so as to be observed from a front side thereof, for example, a hologram sticker to be attached from a back side, in which a transparent adhesive layer, a hologram layer and a light transmission suppressing layer are laminated, is known (for example, see Patent Document 2). This light transmission suppressing layer has a dark color, and suppresses transmission of visible light toward a back surface of the hologram layer so as to enhance the visual contrast of a hologram image. Accordingly, when being observed from the transparent adhesive layer side, which is attached to the object, the hologram layer easily can be identified visually with the light transmission suppressing layer in its background. In addition, as the light transmission suppressing layer, a plastic film and the like that are colored by a dye or a pigment as appropriate can be used.
Whereas, a sharp image is formed in a film by a method including: disposing a transfer paper with an image formed thereon by an ink containing a sublimable dye on a surface of a white film layer of a laminate of the white film layer having no affinity with the sublimable dye and a transparent film layer so that the transfer paper and the white film layer may be in contact with each other; and heating them, whereby the dye is sublimated, penetrates the white film layer and diffuses in the transparent film layer so as to form an image (for example, see Patent Document 3).
In addition, another method is exemplified, which includes: printing, with the ink containing the sublimable dye, on a releasable ink jet receptive layer of a laminate including the ink jet receptive layer, a surface resin layer having no affinity with the sublimable dye and a dye fixing layer that are laminated in this order; subsequently heating the laminate so as to sublimate the sublimable dye, allow the sublimable dye to migrate into the dye fixing layer and form an image in the layer; and then removing and releasing the ink jet receptive layer (for example, see Patent Document 4). However, in the vehicle-identifying sticker of Patent Document 1 that is attached to an object, a self-destructive layer, a print layer including text information or the like and a support layer are provided in this order, when being observed from the object. Accordingly, if the support layer is shaved off by any means while the sticker is attached, the print layer can be reached. Thus, there is a problem that, if the print layer is further shaved off, and the text information or the like is modified using a means such as an ink for marker pens, subsequently, another print layer is newly formed, and the sticker can be counterfeited from its back surface side without being released.
In addition, the vehicle-identifying sticker of Patent Document 1 also has a problem that, even if the print layer is formed on the self-destructive film in order to avoid the above-described problem, an authenticating pattern such as a hologram used as the self-destructive layer is shielded by the print layer and thus is difficult to identify when being observed from the object. Then, since it is difficult to distinguish a sticker having a print layer including counterfeited text information or the like from the vehicle-identifying sticker of Patent Document 1 when being observed from the object, the thus counterfeited sticker is likely to be used with ease.
In addition, in the hologram sticker to be attached from a back side of Patent Document 2 that is attached onto an object, a transparent adhesive layer, a hologram layer and a light transmission suppressing layer are provided in this order, when being observed from the object. Accordingly, Patent Document 2 does not refer to forming an image such as text information, and even if an image is formed, the image is difficult to identify, because the dark-colored light transmission suppressing layer lies in its background.
Moreover, a film in which an image is formed according to Patent Documents 3 and 4 has a problem that sharpness of the image deteriorates over the course of time.
Patent Document 1: JP 2002-366036 A
Patent Document 2: JP 2000-206884 A
Patent Document 3: JP 9(1997)-277731 A
Patent Document 4: JP 2002-79751 A